The present disclosure relates to a seat frame provided at a vehicle seat on which an occupant sits, and particularly to a seat frame which is formed by combining frame sections made of a resin material.
In general, a vehicle seat is configured in such a manner that a cushion material is provided on a frame serving as a framework and that this cushion material is covered with a surface material. This frame serving as a framework is usually configured by a seat cushion frame serving as a framework of a seating portion and by a seat back frame serving as a framework of a backrest. A rear end of the seat cushion frame and a lower end of the seat back frame are attached directly or indirectly (indirectly, for example, via a reclining mechanism) to each other, thereby forming the frame. These frames are provided with not only structures serving as frameworks but also various members, and these members achieve various functions. As to function to support an occupant as described above, for example, an attachment portion to which a headrest for holding the head of the occupant is generally formed at an upper side of the seat back frame.
In order to form such frame, the frame requires high rigidity in view of supporting the weight of the occupant. In addition to this requirement, a reduction in weight of the vehicle seat itself is required; therefore, the technical development to meet both requirements which are generally contradicting has been needed. Under such circumstance, a technique to achieve both the weight reduction and rigidity of the frame has been proposed (for example, refer to Japanese Patent Publication JP 2011-001008A). According to the technique described in Japanese Patent Publication JP 2011-001008A, a diagonal tension wire is arranged at the outer side of a side frame forming a seat back frame and at the outer side of a side frame forming a seat cushion frame, thereby supporting an amount of difference between an impact load acting toward the vehicle front side and an impact load acting toward the vehicle rear side. Further, a closed cross-sectional structure is provided around a rim at a vehicle rear end portion of the side frame to extend in the vehicle up to down direction; thereby, the minimum radius of gyration is locally increased. With the structure just described, the frame rigidity can be secured by the technique according to Japanese Patent Publication JP 2011-001008A. Furthermore, a reinforcement component other than the light diagonal tension wire is not necessary, therefore contributing to weight reduction.
Moreover, from the perspective of formability and lightweight properties, a resin material has tended to be used as a material of a frame in recent years (for example, refer to Japanese Patent Publication JP 2004-322881A). In the technique of Japanese Patent Publication JP 2004-322881A, an inner half member and an outer half member which are formed of resin molded products are assembled to each other; thereby, a frame having a closed hollow cross-sectional shape is formed. In addition, such assembling is implemented by vibration-welding elongated projections for welding which are formed at the outer half member to a receiving portion for welding which is formed at the inner half member. Thus, in the technique according to Japanese Patent Publication JP 2004-322881A, a light resin material can be used instead of a metallic material; therefore, weight reduction can be achieved.
As described above, in a seat frame, both strength and weight reduction are desirable. In the technique of Japanese Patent Publication JP 2011-001008A, the diagonal tension wire needs to be arranged, therefore increasing the number of components and resulting in deterioration of manufacturing workability. Further, it takes time in forming, for example, forming the closed cross-sectional shape at the rim. Furthermore, as in Japanese Patent Publication JP 2004-322881A, a seat frame is formed by resin; thereby, weight reduction can be achieved. However, the rigidity of resin is lower than that of metal; therefore, the aspect of rigidity needs to be further elaborately designed.
In particular, the seat frame having a closed hollow cross-sectional shape has an empty space inside, therefore requiring to be further elaborately designed in order to secure rigidity. In recent years, from the perspective of formability and lightweight properties, a resin material has been used as a material of a seat frame. A frame body formed by such resin material may be configured in such a manner that an inner half member and an outer half member, which are formed of resin molded products, are assembled to each other to form a closed hollow cross-sectional shape. Under such circumstance, necessarily, the seat frame is formed by the resin material to achieve weight reduction and to secure higher rigidity.